Thanks to two orbiting X-ray observatories, astronomers have the first
strong evidence of a supermassive black hole ripping apart a star and
consuming a portion of it.

The event, captured by NASA's Chandra and ESA's XMM-Newton X-ray
Observatories, had long been predicted by theory, but never confirmed.

Astronomers believe a doomed star came too close to a giant black hole
after being thrown off course by a close encounter with another star. As it
neared the enormous gravity of the black hole, the star was stretched by
tidal forces until it was torn apart. This discovery provides crucial
information about how these black holes grow and affect surrounding stars
and gas.

"Stars can survive being stretched a small amount, as they are in binary
star systems, but this star was stretched beyond its breaking point," said
Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics
(MPE) in Germany, leader of the international team of researchers. "This
unlucky star just wandered into the wrong neighborhood."

While other observations have hinted stars are destroyed by black holes
(events known as "stellar tidal disruptions"), these new results are the
first strong evidence. Evidence already exists for supermassive black holes
in many galaxies, but looking for tidal disruptions represents a completely
independent way to search for black holes. Observations like these are
urgently needed to determine how quickly black holes can grow by swallowing
neighboring stars.

Star Ripped Apart by Giant Black Hole

Observations with Chandra and XMM-Newton, combined with earlier images from
the German Roentgen satellite, detected a powerful X-ray outburst from the
center of the galaxy RX J1242-11. This outburst, one of the most extreme
ever detected in a galaxy, was caused by gas from the destroyed star that
was heated to millions of degrees Celsius before being swallowed by the
black hole. The energy liberated in the process was equivalent to a
supernova.

"Now, with all the data in hand, we have the smoking gun proof that this
spectacular event has occurred," said coauthor Günther Hasinger, also of
MPE.

The black hole in the center of RX J1242-11 is estimated to have a mass of
about 100 million times Earth's Sun. By contrast, the destroyed star
probably had a mass about equal to the Sun, making it a lopsided battle of
gravity. "This is the ultimate David versus Goliath battle, but here David
loses," said Hasinger.

The astronomers estimated about one percent of the star's mass was
ultimately consumed, or accreted, by the black hole. This small amount is
consistent with predictions that the momentum and energy of the accretion
process will cause most of the destroyed star's gas to be flung away from
the black hole.

XMM-Newton Spectrum & Illustration of RX J1242-11

The force that disrupted the star in RX J1242-11 is an extreme example of
the tidal force caused by differences in gravity acting on the front and
back of an object. The tidal force from the Moon causes tides in Earth's
oceans. A tidal force from Jupiter pulled Comet Shoemaker-Levy apart,
before it plunged into the giant planet.

The odds stellar tidal disruption will happen in a typical galaxy are low,
about one in 10,000 annually. If it happened at the center of the Milky Way
Galaxy, 26,000 light-years from Earth, the resulting X-ray outburst would
be about 50,000 times brighter than the brightest X-ray source in our
galaxy, beside the Sun, but it would not pose a threat to Earth.

Other dramatic flares have been seen from galaxies, but this is the first
studied with the high-spatial resolution of Chandra and the high-spectral
resolution of XMM-Newton. Both instruments made a critical advance. Chandra
showed the RX J1242-11 event occurred in the center of a galaxy, where the
black hole lurks. The XMM-Newton spectrum revealed the fingerprints
expected for the surroundings of a black hole, ruling out other possible
astronomical explanations.

In the future, searches using Chandra, XMM-Newton and survey instruments
should find many other tidal disruptions. Detailed studies with future
observatories like Constellation-X should teach us about the extreme
physics around supermassive black holes.

NASA's Marshall Space Flight Center, Huntsville, Ala., manages the
Chandra program for the Office of Space Science, NASA Headquarters,
Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW,
Inc., was the prime development contractor for the observatory. The
Smithsonian Astrophysical Observatory controls science and flight
operations from the Chandra X-ray Center in Cambridge, Mass. XMM-Newton
is an ESA science mission managed at the European Space Research and Technology Centre (ESTEC) in the Netherlands for the Directorate of the Scientific Programme.